1. Field of the Invention
The invention relates to airbags for vehicles. More particularly it relates to devices which determine if the airbag was set off in an accident.
2. Brief Description of the Prior Art
Airbags have proven effective in preventing drivers and passengers from being impaled on steering columns, smashed against dashboards and ejected through windshields during vehicular accidents. However in several cases of cars equipped with airbags where the airbags have been deployed, the driver of the vehicle has claimed that the airbag went off inadvertently and caused him to have the accident. There have been reports of inadvertent deployments of the airbags caused by radio interference.
Present airbag systems have no device for positively determining whether the airbag was set off by the sensor in response to an accident at the time the airbag was deployed or if it somehow went off by itself. This information is essential in determining the manufacturer's liability in the event the passenger asserts that an airbag caused the accident. The correct determination of liability is vital to the manufacturer's survival.
Some airbag systems have a diagnostic system which indicates whether an electrical current was sent to the inflator after an accident was sensed, but this does not positively indicate that the gas generator was started after an accident occurred.
A device has been disclosed in U.S. Pat. No. 3,915,474 by Held et. al. for solving this problem. This "recording mechanism for a safety device used in a motor vehicle" has not been adopted due primarily to its large size. A recording mechanism of this type to be usable must not contribute significantly to the size or weight of the airbag system. Any attempt to miniaturize this device, however, results in a problem that in some vigorous crashes the piston will rebound off the end of the cylinder and return to its initial position before the gases from the inflator have had time to arrest the motion of the sensing mass. Thus, in a miniaturized version, the device can give a false reading. The problem arises from the fact that it takes as much as 15 milliseconds from the time the sensor has indicated that the airbag should be deployed and the time that there is significant gas pressure in the inflator.
The present invention represents an improvement over the prior art described in U.S. Pat. No. 3,915,474 in that it uses the primer or squib gas to stop the motion of the sensing mass or pistons. This gas pressure is available in 1 to 2 milliseconds after sensor firing.